1. Field of the Invention
The invention relates to a fuel supply installation in the form of a common-rail system of an internal combustion engine having a plurality of cylinders, in particular a large diesel internal combustion engine operated preferably with heavy oil, wherein the fuel is conveyed by a pumping device from a low-pressure region into a high-pressure region, the high-pressure region comprising a pressure-accumulator line consisting of at least two separate accumulator units connected to one another by means of feed lines, and fuel injectors for the cylinders are connected to the accumulator units. The invention also relates to individual components of a common-rail system which are suitable in a particularly advantageous way for use in a fuel supply installation according to the invention.
2. Description of the Related Art
This fuel supply installation is to be used, in particular, in large diesel internal combustion engines operated with heavy oil. As is known, because of the problematic corrosion and viscosity properties of heavy oil (tendency to paraffin separation, particularly at low temperature, when the internal combustion engine is in the state of rest), the engine and the fuel supply installation have to satisfy special preconditions. Conventionally, therefore, when a fuel supply installation suitable for heavy-oil operation is used, there is a change-over to operation with diesel fuel before the engine stops, so that the feed lines and the components of the fuel supply installation, such as high-pressure pumps, pressure-accumulator line or fuel injectors, still contain only diesel which presents no problems as regards viscosity and paraffin separation. It is also known to heat up the heavy oil itself and the fuel injectors during lengthy rest periods by means of heating and thus prevent paraffin formation.
U.S. Pat. No. 6,240,901 discloses such a fuel supply installation. The functioning of the fuel injectors is controlled electronically, in particular by means of magnetic valves, in order to ensure sufficiently brief and accurate injection. This addresses the problem involved in using a common-rail system in a large diesel internal combustion engine in terms of a constant accumulator pressure (pressure waves) for all the cylinders along the engine axis on account of the length of the pressure-accumulator line which is necessary in this case. Consequently, a pressure-accumulator line consisting of at least two separate accumulator units connected to one another by means of connecting lines has already been produced, the accumulator units being capable in each case of being connected to at least two fuel injectors and in each case of being acted upon by a separate high-pressure pump.
Nevertheless, when the engine is in operation, problems continue to be expected, particularly with regard to the strength of the individual accumulator units, since the feed lines connecting them to one another issue as radial bores and form weak points there and therefore put at risk the stability of the common rail. Furthermore, a greater flexibility in the assembly of the components of the fuel supply installation would be desirable, since the number of accumulator units is linked to the number of high-pressure pumps and their assignment cannot be selected according to the existing space availability, particularly where retrofit solutions are concerned. Moreover, pumps with large stroke volumes have had to be used hitherto, in order to ensure a sufficiently large feed quantity and a sufficiently high feed pressure. This results, in turn, in considerable dynamic pressure fractions, such as pressure hammers and pressure pulsations, which give rise, in turn, to high mechanical loads on the feed lines which entail a considerable risk of damage, such as leakages or breaks.
The invention is intended to eliminate all these above-described disadvantages of the previous fuel supply installation, in particular for large diesel internal combustion engines operated with heavy oil. The object of the invention, therefore, is to provide improved components of the common-rail system which are suitable, in particular, for use in such a fuel supply installation, so that a space-saving, flexible, but nevertheless modular construction becomes possible and, moreover, the operating reliability of the complete fuel supply installation is increased in relation to the prior art.
This object is achieved, according to the invention, by means of each individual accumulator unit of the pressure-accumulator line being designed in such a way that they each have an accumulator volume for serving at most approximately two cylinders. The position of an accumulator unit along the internal combustion engine and its length can therefore be selected in such a way that the shortest possible pressure-accumulator line can be constructed. In a particularly preferred way, an accumulator unit is designed in such a way that it has in each case an accumulator volume for serving two cylinders. By accumulator covers being provided in each case on both end faces, all the functional units are integrated into these in terms of fuel delivery and transfer, retrofitting on existing engine types with common-rail injection systems has been markedly simplified. All the hydraulic connections, and holding devices for positioning the accumulator units along the internal combustion engine, and also sealing-off elements for the accumulator unit, as well as functional units, such as a quantity-limiting valve, are located in the accumulator cover, so that a modular construction becomes possible in a simple way and, furthermore, operating reliability is increased, since the accumulator units, and therefore the entire pressure-accumulator line, are free of external forces which originate from holding devices and hydraulic connections which are now received by the accumulator covers designed according to the invention.
Finally, what is also achieved by arranging at least one separate pump accumulator in the high-pressure region between the high-pressure pump and the assembled pressure-accumulator line, the pump accumulator being connected to at least one accumulator cover of an accumulator unit of the pressure-accumulator line for fuel conveyance and being capable of being acted upon by at least one high-pressure pump, is that the dynamic pressure fractions generated by the pumps can be reduced considerably before the conveyed fuel, that is to say, for example, the heavy oil, is fed into the pump lines which ultimately lead into the pressure-accumulator line. Thus, furthermore, the mechanical load on the accumulator units is markedly reduced and the operating reliability of the entire fuel supply installation is increased.
Since the accumulator volume of each accumulator unit amounts approximately to 50 to 500 times the required injection quantity per cylinder and work cycle, a modular construction of the pressure-accumulator line is promoted in a particularly advantageous way.
In an advantageous embodiment of the invention, the accumulator units of the pressure-accumulator line are connected one behind the other in the throughflow direction via the feed lines, that is to say are capable of being acted upon in series by fuel.
It is to be seen as a further advantageous embodiment of the fuel supply installation that the accumulator units of the pressure-accumulator line can receive line pipes which are laid in the axial direction and which have throttle bores, so that all the accumulator units can be acted upon in parallel by fuel.
It is to be considered as a particularly advantageous measure, furthermore, that the accumulator units are designed with an axial length which, with respect to the axis of the internal combustion engine, corresponds to the cylinder spacing with a tolerance of +/xe2x88x9220%.
The fuel supply installation according to the invention 15 is suitable for all types of large diesel engines, in particular for internal combustion engines operated with heavy oil. The accumulator unit according to the invention, the pumping device and the scavenging device according to the invention are suitable for all types of common-rail injection systems, but, in combination, perfect the fuel supply installation according to the invention.
Other objects and features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the invention, for which reference should be made to the appended claims. It should be further understood that the drawings are not necessarily drawn to scale and that, unless otherwise indicated, they are merely intended to conceptually illustrate the structures and procedures described herein.